We don't have synonyms for regio yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are regid, rego and regis.
(n) :
(astronomy, geology, planetary geology) Any large area of a planet or moon that is strongly differentiated from neighbouring areas by colour or albedo.
(n) :
(astronomy, geology, planetary geology) Any large area of a planet or moon that is strongly differentiated from neighbouring areas by colour or albedo.